The present invention relates to a rotational angle detecting apparatus and a torque detecting apparatus comprising one or a plurality of targets provided at a rotor and a plurality of detection means disposed opposite to the targets, for outputting detection signals having phases different from each other in accordance with each position of the targets as the rotor rotates.
As a steering apparatus for automobiles, an electric power steering apparatus, which drives an electric motor to assist steering and reduce driver's load, is known. Such electric power steering apparatus comprises an input shaft joined to steering member (steering wheel), an output shaft joined to steerable wheels via a rack-and-pinion or the like and a connection shaft that connects the input shaft to the output shaft. On the basis of torsion angle, which is generated on the connection shaft, the torque sensor detects the steering torque applied to the input shaft. And on the basis of the steering torque detected by the torque sensor, the electric motor for assisting the steering, which is interlocked with the output shaft, is controlled to drive. The present applicant has proposed a rotational angle detecting apparatus and a torque detecting apparatus suitable for steering apparatus for automobiles (Japanese Patent Application Laid-Open No. 2003-83823).
Further, the present applicant has proposed a rotational angle detecting apparatus and a torque detecting apparatus equipped with the rotational angle detecting apparatus (torque sensor) (Japanese Patent Application No. 2003-344188). That is, the rotational angle detecting apparatus comprises two detection means, which are disposed respectively opposite to first targets provided at a rotor and second targets provided at the rotor, the number of the second targets is coprime with the number of the first targets; the two detection means output detection signals having phases different from each other as the rotor rotates. The rotational angle detecting apparatus further comprises calculating means for executing a predetermined calculation using the detection signals each outputted by the two detection means and storing means for storing the relation between the result of calculation executed by the calculating means in advance and the electrical angles of detection signals, in which, on the basis of the result of calculation executed by the calculating means and by referring to the storing means, an electrical angle of the detection signals is obtained, and on the basis of the obtained electrical angle, the rotational angle of the rotor is detected.
In the rotational angle detecting apparatus and the torque detecting apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2003-344188, for instance, one of the detection signals is approximated to a sine wave and the phase contrast is set to 90° (Accordingly, the other detection signal is approximated to cosine wave), the rotational angle θ is obtained from θ=tan−1θ=tan−1 (sin θ/cos θ). However, the detection signals include some errors such as ripples. When the calculation such as sin θ/cos θ is executed using the detection signals including the errors, the errors included in the result of the calculation become larger than the original errors. Therefore, there resides such a problem that rotational angle is hardly obtained precisely.